An anthraquinone process, an electrolytic process, an isopropyl alcohol oxidation process and the like have been known as a process for the production of hydrogen peroxide, and the anthraquinone process has mainly been adopted commercially. In this process, an anthraquinone derivative is reduced and oxidized in a nonaqueous solvent system to produce hydrogen peroxide which is then extracted with water and distilled to give a product. This process is not always ideal for producing hydrogen peroxide due to drawbacks such as complexity of the process or a deterioration in the anthraquinone solution.
In order to solve the above-described problem, a number of proposals have been made on a process for producing hydrogen peroxide directly from hydrogen and oxygen. For example, Japanese Examined Patent Publication (Kokoku) No. 56-47121 proposes a process for producing hydrogen peroxide wherein hydrogen oxide is produced in an aqueous acidic solution in the presence of a catalyst comprising a hydrous silicic acid carrier and 5% palladium supported thereon. In such a reaction system, however, it is difficult to avoid elution of palladium as the catalyst from the carrier, so that the proposed process has a problem of the service life of the catalyst. In U.S. Pat. No. 4,681,751, activated carbon is used as the carrier to prepare a palladium-containing metallic catalyst for the production of hydrogen peroxide. Activated carbon has a high capability of adsorbing palladium, so that the elution can be relatively suppressed. However, the effect attained by this method is not satisfactory. In Japanese Unexamined Patent Publication (Kokai) No. 3-103310, an amino acid exists in a reaction medium to reduce the elution of iron ions from a reactor for the purpose of improving the selectivity of hydrogen to hydrogen peroxide. The effect attained by this method too is not satisfactory. An attempt to improve the selectivity of hydrogen to hydrogen peroxide has been made by using, as the catalyst, carrier, cerium oxide in Japanese Unexamined Patent Publication (Kokai) No. 4-238802, lanthanum oxide in Japanese Unexamined Patent Publication (Kokai) No. 4-285003, crystalline silica or a zeolite having a high silica content in Japanese Unexamined Patent Publication (Kokai) No. 5-17106 or a mixed oxide comprising zirconium oxide and vanadium oxide in Japanese Unexamined Patent Publication (Kokai) No. 5-70107. However, none of the above proposals could provide a catalyst having a performance on a practical level. Further, it is known that in general the selectivity of hydrogen to hydrogen peroxide remarkably lowers with increasing the amount of the catalyst. Moreover, the reaction should be carried out in a system having a hydrogen concentration of not more than 4% from the viewpoint of avoiding an explosion of hydrogen gas. It is known that the catalyst is likely to be oxidized under the above condition to cause a lowering in activity and selectivity.
An object of the present invention is to solve the problems of elution of the platinum-group metal, a lowering in activity and selectivity and the like and to provide a process for producing hydrogen peroxide catalytically in a reaction medium with a high catalytic activity and a high selectivity.